Fused-ring and Bicyclic Azasugars

4 Fused-ring and Bicyclic Azasugars. - Four new polyhydroxypyr-rolizidines, the Hyacinthacines Ai, A2, A3 and B3 (118-121 respectively) were isolated from the bulbs of Muscari armeniacum, and their structures elucidated. Bis-aziridine 37 (see Section 1.3.1), derived from D-mannitol, was converted 

5-Isoxazolidinone 124 was synthesized from dehydroamino acid 123, which has a pentose sugar moiety at its side-chain, by displacement of the terminal mesylate by hydroxylamine with spontaneous cyclization by intramolecular Michael-like addition. Interestingly, when a tetrose-derived dehydroamino acid was substituted, no cyclization was observed.  

Improved syntheses of (-l-)-lentiginosine (125) and (7R)-7-hydroxylen-tiginosine (126), inhibitors of amyloglucosidases, have been reported. In multi-step syntheses based upon a 1,3-dipolar cycloaddition of a pyrrolidine N-oxide derived from L-tartaric acid to 3-buten-l-ol, 125 and 126 were prepared in 25% and 37% overall yields from a common indolizidine intermediate. The enantiomers of these compounds could be similarly prepared using D-tartaric acid as a starting material.  

Castanospermine analogues 127 and 128 have been synthesized in many steps from a chirally unresolved pyrrolidinone.  

Bicyclic polyhydroxylated isoquinuclidines with conformations that mimic the boat-form of pyranosides have been prepared in multiple steps from an achiral pyridinone. These compounds proved to be strong and selective inhibitors of snail P-mannosidase (130 R = H, K 20 pm R = Bn, Ki 0.17 pm).  

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